1. Field of the Invention
The present invention relates to the use of coherent energy processes for high powered pulse lasers, in the shock processing of solid materials, and more particularly, to methods and apparatuses to accurately control the laser peening process (i.e., the laser shock process) in a production environment.
2. Description of the Related Art
Known methods of shock processing solid materials and particularly laser shock processing solid materials using coherent energy, as from a laser, orient the laser beam normal, i.e., perpendicular, to the workpiece.
Particular constraints of laser processing are formed based on the shape of material or other geometric factors such as, attempting to laser shock harden integrally bladed rotors (IBRs), blind bores, slots, or dove-tailed sections. The laser beam utilized may not have a direct line-on-sight access to the area to be shock processed. Laser shock processing techniques and equipment can be found in U.S. Pat. No. 5,131,957 to Epstein.
Production problems occur with the placement and location of the workpiece to be processed. Particular pieces of information such as knowing the present and actual location of the workpiece, along with determining whether the laser shock processing system has hit the workpiece where the control program has instructed the laser to do so are important to part quality and reproducibility of results.
What is needed in the art is an automatic system for determining and controlling laser shock process variables.
According to the present invention, the laser shock system utilizes a computerized system for identifying that a workpiece is in a correct placement attitude, and that the laser shock processed operation was conducted at a correct location on the workpiece.
The invention, in one form thereof, is that of a tool fixture, to hold the workpiece to be worked (i.e., laser shock processed). Based upon particular physical characteristics of the tool fixture, the present invention and system can readily identify the location of the fixture based upon reference or locator spots thereon.
A laser processing environment may contain conditions where visibility, at least to the visible light spectrum, may be diminished. The system can also utilize and target areas on the fixture by reference spots, reflectors, LEDs, or other types of indicators, for location within the process environment.
Additionally, positioning encoders may be affixed with the fixture movement means to identify the location of the fixture and workpiece at all times. Such position encoders would actually be just initial or absolute reference markers, since there would still be a need for measuring a reference mark for error trapping and system feedback control.
Another feature of the present invention is that the system can identify, via a number of different means, the focus or angle of the beam shot, and triangulate same from distance calculation based upon the tool fixture reference spots. Such identification can determine whether or not the laser beam moves out of a particular range, thereby causing the laser shock processing system to stop processing and alert the operator, or to utilize such data to automatically re-align the workpiece on the laser beam. In the most preferred case, the absolute location of the laser spot shall stay substantially immovable, while the tool fixture and workpiece are moved to reposition the laser spot on the workpiece.
Yet another feature of the present invention is that of using a video camera to capture the location of the workpiece and fixture. Utilizing image-grabbing software, along with filters to prevent burn out of the video camera, the system may measure the location of the tool fixture at one or more different frequencies to store and analyze data regarding the laser shock processed spot or beam reflection. Additionally, the imaging system of the present invention utilizing a video camera, may be able to detect whether or not a sufficient plasma has formed during the laser shock processing operation to sufficiently work the workpiece. Additionally, the video camera can be used to detect whether or not the transparent overlay utilized in a laser shock processing operations system has been properly created.
Other variables of the laser shock processing system may be determined by the inventional imaging system such as, whether or not there is any transparent or opaque overlay applied to the workpiece, and determining whether or not the proper laser spot size was applied to the workpiece. Of course, other variables may be detected and utilized such as, whether or not the opaque overlay was correctly placed and are of the correct thickness.
The video imaging aspect of the present invention utilizes elements to ensure capture of the laser beam to prevent ghosts and other spurious signals in the digitized data stream. In one aspect of the invention, the digital camera is synchronized to the frame rate and/or the speed of the laser beam. If the camera frame rate is not synchronized to the laser, the camera may observe a portion of the laser spot on more than one frame.
The invention, in one form thereof, is an image processing system for monitoring a laser shock process. The processing system includes a laser shock processing system having a workpiece positioner and a laser shock process system controller, a video camera for forming an electronic image of at least a portion of the workpiece, and an image processing computer connected to the video camera and the laser shock processing controller, the image processing computer including a program to determine a position f the workpiece.
The invention, in another form thereof, is an image processing system comprising a laser shock processing system for creating a laser spot on the workpiece. The laser shock processing system has both a workpiece positioner and a system controller. A video camera is included for forming an electronic image of at least a portion of the workpiece. An image processing computer is connected to the video camera and the laser shock processing controller, image processing computer including a program to determine the laser spot size on the workpiece during laser shock processing.
The invention, in yet another form thereof, comprises a laser shock processing system having both a workpiece positioner and a laser shock processing system controller, a video camera for forming an electronic image of at least a portion of the workpiece, and an image processing computer connected to the video camera and the laser shock processing controller, the image processing computer including a program to determine the position of the laser spot on the workpiece during laser shock processing.
The invention, in still another form thereof, is an image processing system for monitoring a laser shock process utilizing overlays. The image processing system includes a laser shock processing system having both a workpiece positioner and a system controller, along with a video camera for forming an electronic image of at least a portion for the workpiece. An image processing computer connected to the video camera and the laser shock processing controller includes a problem to determine if one of the laser shock processing process overlays is applied correctly to the workpiece during laser shock processing.
The invention, in another form thereof, is a method of controlling a laser shock processing system utilizing dual-sided processing. The method comprises the steps of applying a laser beam to opposite sides of a workpiece, determining the size of the laser spots on each side of the workpiece via an image processing system, and adjusting at least one of the laser spot sizes to then crate a substantially equal sized laser spot on each side of the workpiece.
In still another form, the invention includes a method of controlling laser shock processing system utilizing dual-sided processing. The method comprises the steps of applying a laser beam to opposite sides of a workpiece, determining the position of the laser spots on each side of the workpiece via an image processing system and adjusting at least one of the laser spot positions to provide laser spots on opposite sides of the workpiece which are substantially concentric with each other along a line through the workpiece.
In yet another form, the invention includes a method of controlling a laser shock processing system utilizing dual-sided processing. The method comprises the steps of applying a laser beam to opposite side of a workpiece, determining the position and size of the laser spots on each side of said workpiece via an image processing system, and adjusting at least one of the laser bemas such that the shock waves generated on substantially opposite sides of the workpiece substantially overlap each other as they pass through the workpiece.
The invention, in still another form thereof, comprises an image processing system for use with a laser shock processing system having a workpiece positioner and controller which communicate together passing information encoding a position of a workpiece. The image processing system includes a video camera for forming an electronic image of the workpiece and a programmed image processing computer connected to the video camera and laser shock processing system controller. The computer is programmed to determine a calculated position of the workpiece based upon the electronic image. The computer determines the difference between the calculated position and the encoded position and sends a signal to the laser shock processing controller system if the difference is greater than a predetermined range.
The invention, in another form thereof, comprises an image processing system for use with a laser shock processing system for creating a laser spot of a particular size on a workpiece. The image processing system includes a video camera for forming an electronic image of at least a portion of the workpiece, and a programmed image processing computer connected to the video camera and laser shock processing system. The computer is programmed to calculate the size of the laser spot by operations on the electronic image. The computer then sends a signal to the laser shock processing system if the calculated spot size is outside of a predetermined range.
The invention, in yet another form thereof, comprises an image processing system for use with a laser shock processing system having an opaque overlay applicator to apply opaque overlay to a workpiece. The image processing system includes a video camera for forming an electronic image of the workpiece and a programmed image processing computer connected to the video camera and laser shock processing system. The computer determined from the electronic image whether the laser shock processing system actually applied the opaque overlay and sends a signal to the laser shock processing system in the event that the computer determined that no opaque overlay was applied.
The invention, in another form, comprises a method of controlling a laser shock processing system utilizing dual-sided processing. The method includes the steps of applying a laser beam to opposite sides of a workpiece, determining the size of the spots on each side of the workpiece created from the laser beams with a video camera, and providing a means to adjust at least one of the spot sizes to then create the same sized spot on each side of the workpiece on a subsequent laser beam impact.
The invention, in another form thereof, comprises a method of controlling a laser shock processing system having a workpiece positioner and a system controller. The method includes the steps of applying an opaque overlay to the workpiece over a first are to be laser shock processed, applying a laser beam to a spot on the opaque overlay at the first area, repositioning the workpiece, and determining the integrity of the opaque overlay at a second area to be laser shock processed using an image processing system the second area adjacent to the first area.
An advantage of the present invention, in one form thereof, provides an automatic process to increase the laser shock process work speed in a production environment.
Another advantage of the present invention is that of increased quality control to determine whether processing conditions meet specifications to ensure that the workpiece is sufficiently laser shock processed for intended application.
A further advantage of the invention, in one form thereof, provides a system able to replicate the laser shock process and to analyze the process in a production environment, and thereby reduce production variations. The system makes processing consistent and repetitive across different laser shock processing hits and different laser shock processed parts.
Another advantage of the present invention is that of enabling replicate processing on different parts. By controlling and observing all variables in the laser shock processing system, repetitive processing with a high degree of repeatability and standardization is possible.
Yet another advantage of the present invention, is that based upon the high value of workpieces such as gas turbine engine blades, on which the newly created imaging system may operate, waste of high-valued workpieces is reduced.
Still another advantage of the present invention, is that it operates in a superior fashion over conventional position encoding of particular gripper or robot arms. The present imaging system gives direct feedback to inform the operator that the laser shock processing system is definitely hitting the spot that it is programmed to hit. Programming a robot to move workpieces in a particular direction does not let you know if the mirrors of the laser are out of alignment, or if the workpiece has moved in the fixture.
Another advantage of the present invention is the ability to determine whether or not the opaque overlay has been applied to the workpiece, thereby preventing scorching of the workpiece surface during laser shock processing.
Another advantage of the present system is creating an automatic alignment technique for double-sided processing of workpieces. Additionally, real time checking of the spot position and spot size is possible during the laser shock processing operation.